1. Field of the Invention
The present invention relates to an organic thin film transistor (TFT) substrate and, more particularly, to a simplified fabrication process for an organic TFT substrate in which two banks for forming a gate insulating layer, an organic semiconductor layer, and a passivation layer are formed by a single bank insulating layer forming process.
2. Description of the Related Art
Typically, a liquid crystal display (LCD) device has liquid crystal cells arranged in a matrix on a liquid crystal panel. The LCD device displays an image by making each of the liquid crystal cells adjust its orientation according to a signal. The orientation of the liquid crystal cells affects light transmissivity through the cells.
A thin film transistor (TFT) is provided for each liquid crystal cell as a switching element, so that each liquid crystal cell is independently supplied with a video signal. An active layer of the TFT may be formed of an amorphous silicon (amorphous-Si) layer or a poly silicon (poly-Si) layer.
The amorphous silicon layer or the poly silicon layer is formed by a complicated fabricating process that entails deposition, photolithography, and etching, leading to a high fabricating cost.
To reduce the cost of preparing an LCD device, efforts have been directed to developing an organic TFT that uses an active layer that can be formed by a simple printing process.
The organic semiconductor layer of the organic TFT overlaps a gate electrode with a gate insulating layer interposed therebetween and is protected by a passivation layer formed on the organic semiconductor layer. In fabricating the organic TFT, the gate insulating layer, the organic semiconductor layer and the passivation layer may be formed by using a printing process.
In order to form the gate insulating layer, the organic semiconductor layer and the passivation layer at their exact locations, the bank for defining the location of the gate insulating layer and the bank for defining the locations of the organic semiconductor layer and the passivation layer are separately formed.
However, a bank insulating layer is formed by using a photo process that is complicated and expensive, and a process for forming the bank insulating layer is performed at least twice to fabricate the conventional organic TFT substrate.
In addition, the conventional organic TFT has a large contact resistance between source and drain electrodes (which are made of an inorganic material) and the organic semiconductor layer (which is made of an organic material) due to a difference in their work functions, and the large contact resistance causes degradation of electrical characteristics of the organic TFT.